I believe the Core i5 processor will be limited to DDR3 ram running at 1333 (10X BCLK multiplier), unless you overclock the BCLK. So unless you plan to overclock, look for ram from a reputable manufacturer that runs at 1333, 1.5v with the lowest timings that you can afford. You will see lots of ram that is marketed for P55 and Lynnfield that runs at higher than 1.5v, but be advised that Intel considers the top of the "normal operational limits" to be 1.575v. Make of that what you will. Alternatively, you could look for ram running at higher speeds and voltages (like 1600 @ 1.65v) at looser timings and just underclock and undervolt it to 1333, 1.5v and tighten up the timings. Whatever's cheaper. All DDR3 will run at 1.5v, just not necessarily at the speed that it's maketed at.
